Row-diagonal parity technique for enabling efficient recovery from double failures in a storage array

Abstract

A “row-diagonal” (R-D) parity technique reduces overhead of computing diagonal parity for a storage array adapted to enable efficient recovery from the concurrent failure of two storage devices in the array. The diagonal parity is computed along diagonal parity sets that collectively span all data disks and a row parity disk of the array. The parity for all of the diagonal parity sets except one is stored on the diagonal parity disk. The R-D parity technique provides a uniform stripe depth and an optimal amount of parity information.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]The present invention is related to the following co-pending and commonly assigned U.S. patent application Ser. No. 10 / 035,603 filed on Dec. 28, 2001 titled, Correcting Multiple Block Data Loss in a Storage Array Using a Combination of a Single Diagonal Parity Group and Multiple Row Parity Groups, which was filed on even date herewith and which application is hereby incorporated by reference as though fully set forth herein.FIELD OF THE INVENTION[0002]The present invention relates to arrays of storage systems and, more specifically, to a technique for efficiently reconstructing any one or combination of two failing storage devices of a storage array.BACKGROUND OF THE INVENTION[0003]A storage system typically comprises one or more storage devices into which data may be entered, and from which data may be obtained, as desired. The storage system may be implemented in accordance with a variety of storage architectures including, but not limit...

AI Technical Summary

Benefits of technology

[0024]The present invention comprises a “row-diagonal” (R-D) parity technique that reduces overhead of computing diagonal parity for a storage array adapted to enable efficient recovery from the concurrent failure of two storage devices in the array. The R-D parity technique is preferably used in an array comprising a number n of storage devices, such as disks, including a row parity disk and a diagonal parity disk, wherein n=p+1 and p is a prime number. The disks are divided into blocks and the blocks are organized into stripes, wherein each stripe comprises n−2 rows. The blocks of the rows selected to form a stripe are typi

Problems solved by technology

In the operation of a disk array, it is anticipated that a disk can fail.

Data can be lost when one or more disks fail, making it impossible to recover data from the device.

Mirroring is an expensive solution in terms of consumption of storage resources, such as disks.

Backup does not protect data modified since the backup was created.

However, if two disks fail concurrently within a parity group, then an unrecoverable loss of data is suffered.

Failure of two disks concurrently within a parity group is a fairly common occurrence, particularly because disks “wear out” and because of environmental factors with respect to the operation of the disks.

A double failure typically arises as a result of a failure of one disk and a subsequent failure of another disk while attempting to recover from the first failure.

If the storage system is busy serving requests, the elapsed time for reconstruction increases.

However, having small parity groups is expensive, as each parity group requires an enti

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